(This article was written in 2009 and uses data from previous years. Expenditure patterns change slowly and the conclusions are likely to be broadly accurate today. I am posting it now because the data is referred to in an magazine article to be published in the next few weeks.)
If we include the full impact of flying, the average person in the UK is responsible for about twelve and a half tonnes of greenhouse gases each year. About half of this total comes directly from running our homes and from personal travel. The rest comes from the things we buy, our carbon dioxide output at work and from manufacturing industry.

In mid November the Prime Minister gave his first speech on climate change. He said that emissions may have to fall by 80% by 2050. This means moving from twelve and a half tonnes per person down to two and a half. Many scientists say that even this is too much and we may eventually have to cut our average emissions to no more than one tonne. This is less than 10% of today's level.

Who is going to find it most difficult to reduce their emissions? What types of families are going to have to make the steepest cuts? We did some work to examine how much carbon dioxide the rich generate compared to the less well-off. The results show that if all of us are going to have to live within a small allowance, the better-off are going to have to really cut back. The richer you are, the more you spend on goods and services that produce carbon dioxide emissions. So, for example, people who don’t have much money don’t fly away on holidays very much. But some people travel by air ten times a year. The wealthiest ten per cent of the country have a carbon dioxide footprint just from motoring of almost two tonnes, enough to use up most of an individual's allowance for 2050. This is over four times the level of the least well-off. When we added up the sums, we found that the richest ten per cent have emissions almost two and a half times as great as people at the other end of the income range.

Our technique.

We used a very good source of government data, the annual Family Spending survey. The information in this huge report is taken from a large number of detailed questionnaires that were completed in 2005 and 2006, the latest year for which data is available. For each group of one tenth ofUKhouseholds, moving from poorest to richest, the survey says what they typically spend on hundreds of different items. For example, you can find out what people in various income groups spend in ice cream, alcopops, children's clothing or even reading glasses. Thousands of people fill in the questionnaire and the numbers are thought to be very accurate.

In the latest report, the top ten per cent of households have an average spending, across all family members, of almost £1,300 a week. The middle-ranked households had an expenditure of about £500, and the people at the lowest income level were spending less than £135 a week.

How did we calculate a carbon footprint?

We looked at the main different types of household expenditure that involve burning fossil fuels. For example, we noted spending of gas and electricity. When you heat your house, the boiler is emitting carbon dioxide to the outside world. Slightly differently, when you turn on the lights, a power station has to burn just a bit more fuel. This means more CO2 up the power station chimney. We also looked at how much people spend on petrol and diesel. If they spend money, it means they bought litres of fuel which are burnt in the engine and carbon dioxide comes out of the exhaust. We also examined the money spent on public transport and flying, though the numbers are slightly less good for aviation than we'd like. Information about foreign holidays is there and, finally, we looked at money spent on meat. Meat is important because animals emit greenhouse gases such as methane and because they eat grains, which have generally required artificial fertiliser to grow. Fertilisers take a lot of fossil fuel to make.

Let's look at the main categories in turn.

Heat and power for the home

People in the top income groups spend a lot more on gas and electricity. The latest data shows the richest 20% of households spending £17 a week on domestic power and heat, while the bills of the poorest 20% were only £9 a week. But richer families have much larger households. Many of the poorest people in theUKlive alone but the top 20% of families have an average of over 3 people in the house. So when we look at spending per person on gas and electricity, we find that it doesn’t vary much across the income groups. The richest people actually have a slightly lower carbon footprint than the less well-off. But there isn’t a big difference between the various groups. This was surprising. Because rich people generally have much bigger houses and more space per person, we thought that they would spend more on fuel per person. This isn’t the case, suggesting that less well-off people may live in houses that are not particularly well insulated.

Interestingly, we also made a calculation about the carbon footprint of the electricity we use. We used standard government numbers to work out what the average emissions are per person. Very roughly, it is just under a tonne each for electricity, and between one and a half and two tonnes for gas. If nothing else, this does show how far we have to go to meet the latest targets set by Gordon Brown.

Petrol and diesel for the car

Whereas there isn’t much difference between income groups when it comes to heat and power, we do see large disparities in fuel use for cars. The richest people spend over four times as much per person as the least well-off. Richer people generally have bigger cars and drive them longer distances. Very roughly, people in the least well-off portion of theUKpopulation have a carbon footprint of less than half a tonne from driving, compared to almost two tonnes among the wealthiest.

Public transport

Public transport expenditure is very interesting. Rail use goes up dramatically as people get wealthier. It is almost ten times as much among the richest as among the people at the bottom end of the spectrum. On the other hand, households with less money actually spend more on bus and coach fares. As we know, most people don’t travel much by public transport, so the impact on total carbon dioxide emissions is not that great.

Air travel

It's here that we see the most striking differences. The numbers are less precise than for car travel, but the richest groups spend over ten times as much on foreign holidays (usually taken by air) and perhaps five times as much on flights. This almost certainly means that the top 10% have a footprint of more than four tonnes from flying compared to well under half a tonne for the least well off group. In a future world in which carbon dioxide is much more carefully controlled, many people's flying habits are going to have to change, or the airlines are going to have to have to find a way of burning less fossil fuel.

Meat

At about £4 per person per week, this doesn’t vary much between income groups, though high income homes do spend a little more. Household diets vary enormously and there isn’t any obvious evidence that the most carbon-intensive food are disproportionately eaten by any one income group.

What does it all add up to?

We have looked briefly at the main carbon culprits – the things which have the greatest impact on your personal responsibility for climate changing gases. We can summarise roughly how emissions vary by income group.

Approximate greenhouse gas emissions per person

(tonnes per year)

Bottom 10%

Average income

Top 10%

Electricity

0.9

0.8

0.9

Gas

1.7

1.6

1.7

Motor fuels

0.4

1.1

1.8

Public transport

0.1

0.1

0.2

Air travel

0.4

1.5

4.0

Meat

0.3

0.3

0.4

TOTAL

3.8

5.4

9.0

Approximate expenditure per person per week

£80

£200

£450

Almost all of the difference is driven by the much higher figures for air and car travel in the highest income groups. The most prosperous people have carbon emissions from these sources of almost two and a half times the least well-off. Add all these numbers up, and the climate emissions vary by almost two and a half times across the income range.